The treatment of a stenosis site to prevent restenosis after angioplasty using radiation is well known. Angioplasty (also referred to as percutaneous transluminal angioplasty (PTA)) is a non-surgical technique for unblocking vascular lumens resulting from peripheral and coronary vascular disease. This technique has become an accepted form of treatment both in the United States and internationally. Another form of treating vascular disease is atherectomy, a surgical procedure for the same purpose of removing stenotic lesions from arteries.
In typical angioplasty procedures, a guiding catheter is percutaneously introduced into the vascular system of a patient's body through an artery. Once inserted, the guiding catheter is maneuvered through the vascular artery until the distal tip of the guiding catheter is positioned proximal to the lesion site. A guide wire and a balloon catheter are then introduced through the guiding catheter. First, the guide wire is advanced through the distal tip of the guiding catheter until the distal end of the guide wire moves past the lesion to be dilated. Then, the balloon catheter is advanced over the guide wire to a location such that the balloon on the distal end portion of the catheter is positioned inside the atherosclerotic narrowing of the artery. The angioplasty procedure may then begin by inflating the balloon to a predetermined size, thereby compressing the atheroma. This enlarges the atherosclerotic narrowing and enlarges the lumen by stretching the vessel wall. After a predetermined period of time, the balloon is deflated and removed.
However, a recurrent problem following angioplasty is that excessive tissue growth may occur at the site of the balloon catheter, thereby causing the development of further blockage or renarrowing of the diseased vessel; this can also occur after an atherectomy procedure. This problem, called restenosis, is thought to be part of a natural healing process after stretching the vascular structure during angioplasty. It is caused by fibrointimal proliferation of the stretched wall in which the cells lining the vascular interior multiply and form fibrous tissue. Restenosis can result in the necessity of repeating the angioplasty or atherectomy procedure.
The successful use of radiation therapy to prevent the growth of such fibrous tissue after an angioplastic or an atherectomy procedure, thereby reducing the tendency for restenosis, is well known. In general, such radiation therapy consists of exposing the stenosis or treatment site to radiation. The effective dose to inhibit restenosis depends on the type of radiation, e.g., Gamma or Beta radiation, as well as the devices and techniques used to deliver such radiation. In addition, the intensity of radiation source on the treatment site drops rapidly as a function of the distance of the radiation source to such treatment site. Accordingly, if the source is not held reasonably near the treatment site of the vascular pathway, the treatment site will receive less than the prescribed dosage of radiation. Under dosing the treatment site will reduce the effectiveness of radiation therapy such that restenosis is not prevented or is even exacerbated. Similarly, the portion of the pathway which is not stenosed but is nearest the radiation source will receive an excess dose of radiation. Application of radiation to a healthy portion of the vessel wall is harmful. For example, overdosing of a section of blood vessel can cause arterial necrosis, inflammation and hemorrhaging. In addition, improper exposure of healthy tissue to radiation may occur not only during the treatment period but also during delivery of the radiation to the treatment site. As a result, while radiation therapy has been found to prevent restenosis, its use must be carefully controlled to maximize exposure to the treatment site while minimizing exposure to healthy portions of the vascular pathway.
The following United States Letters Patents disclose various embodiments for radiation therapy: U.S. Pat. No. 5,643,171 to Bradshaw et al.; U.S. Pat. No. 5,498,227 to Mawad; U.S. Pat. No. 5,484,384 to Fearnot; U.S. Pat. No. 5,411,466 to Hess; U.S. Pat. No. 5,302,168 to Hess and U.S. Pat. No. 5,213,561 to Weinstein et al. These patents are incorporated in their entireties herein by reference. The devices and methods described in the foregoing patents in general expose a stenosis site to radiation using two general approaches. For the first general approach, a catheter includes a structure at its distal end which functions to expose the treatment site to radiation (hereinafter referred to as an exposure structure). Examples of such exposure structures are ventilation features (such as apertures or slits) in the catheter or in a balloon attached to such catheter, or a helical spring, expandable cage or other wire structure. In addition, the catheter contains a treatment channel used for delivering the radiation source to the catheter's distal end. Using this approach, the distal end of the catheter can be precisely positioned at the treatment site before delivering the radiation source. Thereafter, the radiation source can be delivered for precise placement at the treatment site such that it maximizes irradiation of the treatment site while minimizing irradiation of healthy tissue in the vascular pathway.
For the second general approach, the exposure structure at the distal end of the catheter (or other carrier device to which the exposure structure can be attached, such as, for example, a guidewire) can have the radiation source attached to it before insertion into the vascular pathway. However, using this approach, the radiation source exposes the healthy tissue of the pathway along the path traversed to deliver such radiation source to the treatment site. Therefore, some known devices and methods have the disadvantage of exposing healthy tissue to radiation as a by-product of irradiating the treatment site.
However, for other known devices and methods of the second general approach, a provision is made for shielding the radiation source in the distal end of the carrier device prior to initiation of irradiation procedure. For example, the exposure structure on which the radiation source is attached is contained within a structure separate from the exposure structure (hereinafter referred to as a shielding structure). The shielding structure in turn does not have any apertures or other ventilation features through which the radiation source can expose the vascular pathway outside such shielding structure. In effect, the exposure structure is housed prior to initiating the irradiation treatment. Then, either the exposure or shielding structure is moved or otherwise manipulated to free the exposure structure from the shielding structure such that the radiation source is exposed to the stenosis site. However, these known devices and methods have the disadvantage of integrating an exposure structure with a shielding structure for use in the procedure. As a result, for example, the combined structures are more rigid. This impacts the physician's ability to track the carrier device through the tortuous arteries because greater rigidity makes maneuvering the carrier device more difficult, resulting in a more complicated procedure. In addition, with two structures, malfunctions of either structure render the irradiation procedure unsuccessful. Thereby, the chance of a successful procedure is decreased.
In addition, where any of the above malfunctions or complications occurs, the period of time that the radiation source is present in the patient's body as well as the length of time required to successfully complete the irradiation procedure will be increased. This results in increasing the patient's exposure to medical risks inherent in the irradiation procedure as well as more general medical procedure risks. The likelihood of additional complications for the patient is thereby also increased.
Accordingly, there is a need to improve the heretofore known devices and methods, in order to overcome the above described shortcomings in the known devices and methods.